The vertebrate retina offers unique advantages for studying the mechanisms of information processing the central nervous system. Although the physiological responses and synaptic connections of the different cell types have been extensively studied, identities of neurotransmitters used by retinal cells are unknown. During the past four years, under the guidance of Dr. Torsten Wiesel, this investigator has studied the synthesis and accumulation of known or suspected transmitters in intact retinas and in identified, dissocated retinal cells (Lam, 1972 a,b, 1973). The main objective of this proposal is to use such a chemical approach to identify the transmitters used by every retinal cell type. There are also 4 other related aims: (1) The stages in the developing tadpole retina during which the synthesis of transmitters are first detected will be determined chemically and will be compared with retinal physiology and morphology at those stages. (2) Glutamate decarboxylase in the goldfish retina will be partially purified and characterized. Possible control of GABA synthesis and metabolism in the retina will aso be examined. (3) Attempts will be made to obtain isolated photoreceptors that are light-responsive. The identity of the receptor transmitter and the mechanism of transmitter release from these cells will then be investigated. The membrane properties and light-induced current and voltage changes in these cells will also be studied by intracellular recordings. (4) The electrophysiological properties of other isolated retinal cells, especially elasmobranch horizontal cells, will be studied. Improved dissociation and cell culture techniques will be used to prepare healthy cells suitable for physiological and pharmacological experiments.